What will increase the Memory size of a Excel

Hello,
I am working on a Excel sheet of 156KB. Unfortunately it is increased to around 5MB. May i know the reason that may happened and how can i retrieve that.

Thank you for your response. I tried that search tool but i couldn't find the solution what i want.

I added one column having data(No formatting, Formula) at few cells. After this size changed from 156KB to 5MB. All data in that column were deleted and make it an 'Empty column'. But size remains same. I got the actual size(size before adding a column) only after removing that column. Can You please help me on this and let me know what kind of action made this happen.